1. Field of the Invention
The invention relates to methods for converting carbonaceous materials into liquid and gaseous products.
2. Related Art
Biomass is the only renewable source of carbon on earth and what is termed “lignocellulosic biomass” or “woody biomass”—material composed almost exclusively of the distinct polymers cellulose, hemicellulose, lignin, and lignocellulose—is the most abundant form of biomass. It is estimated that 1.3×1012 kg/yr of these materials could be sustainably produced in the United States without compromising the supply of building materials or food. As of April, 2005 production of these materials was roughly 1.8×1011 kg/yr in the United States (1).
Historically there are three approaches to the production of liquid fuels and commodity chemicals from woody biomass: gasification, pyrolysis, or hydrolysis (2). Pyrolysis and gasification involve heating raw biomass to select for either liquids or gases, respectively. They are non-selective processes. They are attractive because they produce a ready-to-go product (in poor yield) such as “bio-oil” or syn gas, the latter of which is attractive because of the large chemical infrastructure already in place for its utilization. However, both processes produce a large quantity of char, which has been described as “the most cumbersome and problematic parameter in any gasification commercialization effort” (3).
Hydrolysis refers to the specific efforts to use near- and supercritical water to convert cellulose and hemicellulose to fermentable sugars and assumes that the lignin thus produced will be treated separately. The problems with hydrolysis are two-fold: water must be separated from the final product, and the chemical bonds that compose woody biomass, especially aryl ethers, are inherently resistant to hydrolysis.
Representative of the state of the art is the flow chart depicted in FIG. 1 (taken from the Huber review, Ref. 2).